Category
Definition
A
Adequate, well-controlled studies in pregnant women have not shown an increased risk of fetal abnormalities in any trimester of pregnancy.
B
Animal studies have revealed no evidence of harm to the fetus; however, there have not been any adequate and well-controlled studies performed in pregnant women.
C
Animal studies have shown an adverse effect; however, there have not been any adequate and well-controlled studies in pregnant women, or no animal studies have been conducted and there have not been any adequate and well-controlled studies in pregnant women.
D
Adequate, well-controlled or observational studies in pregnant women have demonstrated a risk to the fetus. However, the benefits of therapy may outweigh the potential risk. For example, the drug may be acceptable if needed in a life-threatening situation or serious disease for which safer drugs cannot be used or are ineffective.
X
Adequate, well-controlled or observational studies in animals or pregnant women have demonstrated positive evidence of fetal abnormalities or risks. The use of the product is contraindicated in women who are or may become pregnant.
Two drugs used in the management of cardiovascular disease are known to be associated with teratogenic effects. Angiotensin converting enzyme inhibitors may lead to tubular dysgenesis and decreased skull ossification (Koren et al. 1998). This may result in prolonged neonatal renal failure. Angiotensin II receptor blockers and direct renin inhibitors should be considered to have the same risks as the ACE inhibitors. In general, ACE inhibitors are regarded as contraindicated during pregnancy. The evidence of malformation arising from the inadvertent use of these drugs in the first trimester is contradictory and prior exposure to ACE inhibitors is not usually regarded as an indication for termination of pregnancy (Rakusan 2010).
Warfarin is a clearly identified teratogen giving rise to nasal hypoplasia when used in the first trimester. It may also cause calcification of the fetal long-bone epiphysis (chondroplasia punctata) (Rakusan 2010). Warfarin will anticoagulate the fetal circulation and increase the risk of fetal haemorrhage. This can result in intrauterine death or the delivery of a neonate with cerebral haemorrhage.
There is evidence that antihypertensive drugs used in the first trimester are associated with a higher risk of fetal disease including Ebstein malformation, coarctation of the aorta, pulmonary valvular stenosis and atrial septal defects. Nevertheless, antihypertensive drugs are mostly classified as FDA category C agents (Caton et al. 2009). Beta-blockers are generally regarded as safe with the exception of atenolol which has been implicated in the development of intrauterine growth restriction.
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